google hangout sending texts twice?

google hangout sending texts twice?

So I'm pretty new to Android, just got a HTC One as I was fed up with Apple and I'm loving it! Such an amazing phone! I have a question which maybe is me doing something wrong. My texts come through the Google hangout app which is good and of course I can reply but it does something weird. When I reply to a text it automatically says not sent and do I want to resend. It does this even if I have a full 3G signal. When I press resend it flies through and sends it straight away. This is fine but the issue is that it's sending messages twice so the recepicant gets 2 texts off me the same??